In a power distribution system, a modularized terminal electric appliance based mainly on a low-voltage breaker is mostly and widely used, and it has the functions of not only controlling ON/OFF of main circuit or equipment, but also applying overload, short-circuit and over-voltage protection on main circuit or equipment. OFF state locking function has become one of the most common and important functions in power management and safety management as the standard of power safety management is continuously raised, this OFF state locking means that moving contacts and fixed contacts of a breaker are locked at a breaking and non-closeable OFF state position. The OFF state locking is mainly used for the breakers in a power distribution system, and when the protective branches of a particular breaker in the power distribution system fail or lead to tripping of the breaker or out-of-work of equipment due to fault, the fault reason needs to be checked and the breaker can be closed and used only after all the faults are eliminated, an operation electrician typically carries out a check at the positions of the protective branches or the position of the equipment far away from the protective breaker in the process of manual fault check, in this case, closing operation of the breaker is not allowed so as to prevent the operation electrician from electric shock, and in order to guarantee the safety of the operation electrician, the handle of the circuit-protecting breaker needs to be locked at the OFF position to prohibit breaker closing and thoroughly cut off the transmission path for power supply, only in this way can the safety of the operation electrician be guaranteed during inspection and maintenance. Furthermore, it is also quite common to implement power limitation management by the OFF state locking function, and in particular, it is often necessary to prohibit a power user from closing operation of the breaker without permission within a certain period of time in public places without continuous power use. The ON state locking means that a breaker is locked under an ON state so that manual opening thereof cannot be accomplished, but this does not interfere with fault tripping. The ON state locking is mainly used for some terminal electric appliances that are not in need of tripping protection function or that the handle thereof can still be located at an ON position after tripping, and its purpose is to avoid, for users having a quite low power failure possibility during load side operation, negative influence on working or damage to equipment caused by random power failure.
There are mainly two known principles for an OFF state locking device: 1, built-in locking device: this locking device is located within a breaker, locking/unlocking of the built-in locking device is achieved by a locking button on the breaker or by a remote controller, and its defects include complex structure, occupation on valuable internal space of the breaker, indirect locking state display, poor locking safety and reliability and the like, so this built-in locking device is not commonly used; 2, external locking device: this locking device can be kept under an OFF state in such a manner that a breaker is locked and cannot be closed by limiting the operation of a breaker handle, and its advantages are simple structure, direct locking state display and excellent locking safety and reliability, thus the external locking device is applied extensively. In terms of structure, the OFF state locking device of the existing modularized terminal electric appliances are approximately classified in two structural types: the first one is detachable OFF state locking device that is primarily applicable for nations and regions in which IEC standard is implemented or definite regulations in relation to the structure of the locking device have not been promulgated, this type of device is advantageous in such facts that its structure is small and skillful and that whether the locking device is mounted on a breaker can be determined conveniently by a user with the help of the detachment function, however, its shortcoming is the non-applicability for UL standard-implementing nations and regions, i.e. definite regulations in relation to the structure of the locking device have been promulgated; the second one is non-detachable OFF state locking device, which is primarily applicable for UL standard-implementing nations and regions, i.e. definite regulations in relation to the structure of the locking device have been promulgated, and undoubtedly, which can also be applied in nations and regions in which IEC standard is implemented or definite regulations in relation to the structure of the locking device have not been promulgated. It is assembled together with a breaker and cannot be randomly detached by a user, and the problem of the current non-detachable handle locking device, which exists generally, is inconformity with the requirements of modularized standard, that is: the height of the locking device is larger than the maximal height of the entire electric appliance during motion of the handle of the terminal electric appliance, thus it cannot adapt to a terminal power distribution box under modularized standard, the height of the locking device beside the handle is larger than the maximal external dimension of the breaker after an inspection or maintenance operation comes to an end, namely after the locking function is cancelled, and in case that the breaker is mounted in the box body, the height of the box body, i.e. the height dimension of a transparent enclosure, must be increased because the height of the locking device is higher than the maximal external dimension of the terminal electric appliance and is also non-adjustable so that covering of the transparent enclosure of the modularized terminal power distribution box cannot be accomplished, and this increase could affect the service compatibility of the device in the power distribution box and the consistency in appearance simultaneously. For example, disclosed in U.S. Pat. No. 7,355,132B1 or US2008/0277250A1 are external handle locking devices, which are both provided with a handle for operating the ON/OFF state of the terminal electric appliance and both include a member that is permanently higher than the maximal external dimension of the breaker; after the locking device and the modularized terminal electric appliance are assembled, a relatively large space is occupied by the structure of the operation panel for the locking device or the device is non-adjustable in height, which not only affects the compatibility and adaptability between the handle locking device and the modularized power distribution box, but also causes tremendous inconvenience to normal closing and opening operations of the breaker under an unlocking state, namely, the handle of the breaker cannot be operated conveniently by fingers, and there are some problems that are not in conformity with the requirements of UL standard.